在没有internet连接的情况下打开应用程序并在iOS上显示警报

import UIKit
import SystemConfiguration

class ViewController: UIViewController {

    override func viewDidLoad() {
        super.viewDidLoad()
        
        // 检测网络连接状态
        if !isInternetAvailable() {
            // 创建警报控制器
            let alertController = UIAlertController(title: "无法连接到Internet", message: "请检查您的网络连接", preferredStyle: .alert)
            
            // 添加一个取消按钮
            let cancelAction = UIAlertAction(title: "取消", style: .cancel, handler: nil)
            alertController.addAction(cancelAction)
            
            // 显示警报
            present(alertController, animated: true, completion: nil)
        }
    }
    
    // 检测网络连接状态
    func isInternetAvailable() -> Bool {
        var zeroAddress = sockaddr_in()
        zeroAddress.sin_len = UInt8(MemoryLayout.size(ofValue: zeroAddress))
        zeroAddress.sin_family = sa_family_t(AF_INET)
        
        guard let defaultRouteReachability = withUnsafePointer(to: &zeroAddress, {
            $0.withMemoryRebound(to: sockaddr.self, capacity: 1) {
                SCNetworkReachabilityCreateWithAddress(nil, $0)
            }
        }) else {
            return false
        }
        
        var flags: SCNetworkReachabilityFlags = []
        if !SCNetworkReachabilityGetFlags(defaultRouteReachability, &flags) {
            return false
        }
        
        let isReachable = flags.contains(.reachable)
        let needsConnection = flags.contains(.connectionRequired)
        
        return (isReachable && !needsConnection)
    }
}